Acrylic or methacrylic resin emulsion coating composition, and its use

Abstract

An acrylic or methacrylic resin emulsion coating composition comprising a blended mixture composed of (1) 100 parts by weight as solid resin content of a copolymer resin emulsion [A], the copolymer resin therein having a glass transition temperature Tg(A), determined by the DSC method, of about -10 DEG to about -55 DEG C., and said copolymer resin emulsion [A] being an aqueous emulsion-copolymerization product being free from a copolymerizable diallyl component and derived from acrylic and/or methacrylic monomers (a) and (b) specified in the claims in the presence of a polyoxyethylene/polyoxypropylene block copolymer, (2) 20 to 300 parts by weight as solid resin content of a copolymer emulsion [B], the copolymer resin therein having a glass transition temperature Tg(B), determined by the DSC method, of less than 0 DEG C., and satisfying the following equation Tg(B)-Tg(A)=10 DIFFERENCE 55 DEG C. and said copolymer resin emulsion [B] being an aqueous emulsion-copolymerization product being free from a copolymerizable diallyl component and derived from acrylic and/or methacrylic monomers (a)' and (b)' specified in the claims in the presence of a polyoxyethylene/polyoxypropylene block copolymer, and (3) about 0.2 to about 10 parts by weight, based on the total weight as solid resin content of emulsions [A] and [B], of a water-soluble polyvalent metal salt (C) of an inorganic or organic acid, the metal salt (C) having a solubility of at least 5 when it is expressed as the grams of said metal salt dissolved in 100 g of water at 20 DEG C.

What is claimed is 
     
       1. An acrylic or methacrylic resin emulsion coating composition comprising a blended mixture composed of (1) 100 parts by weight as solid resin content of a copolymer resin emulsion [A], the copolymer resin therein having a glass transition temperature Tg(A), determined by the DSC method, of -10° to about -55° C., and said copolymer resin emulsion [A] being an aqueous emulsion-copolymerization product being free from a copolymerizable diallyl component and prepared by emulsion copolymerization of from 95 to 99.5% by weight of at least one monomeric ester (a) of at least one of acrylic and methacrylic acid and 0.5 to 5% by weight of at least one alpha,beta-unsaturated carboxylic acid (b) in the presence of, as a nonionic surface-active agent, a polyoxyethylene/polyoxypropylene block copolymer,   (2) 20 to 300 parts by weight as solid resin content of a copolymer resin emulsion [B], the copolymer resin therein having a glass transition temperature Tg(B), determined by the DSC method, of less than 0° C., and satisfying the following equation   10° C.≦Tg(B)-Tg(A)≦55° C.     and said copolymer resin emulsion [B] being an aqueous emulsion-copolymerization product being free from a copolymerizable diallyl component and prepared by emulsion copolymerization of from 95 to 99.5% by weight of at least one monomeric ester (a)' of at least one of acrylic and methacrylic acid and 0.5 to 5% by weight of at least one alpha,beta-unsaturated carboxylic acid (b)' in the presence of, as a nonionic surface-active agent, a polyoxyethylene/polyoxypropylene block copolymer, and     (3) about 0.2 to about 10 parts by weight per 100 parts of resins, as solids, of emulsions [A] and [B] combined, of a water-soluble polyvalent metal salt [C] of an inorganic or organic acid, the metal salt [C] having a solubility of at least 5 when it is expressed as the grams of said metal salt dissolved in 100 g of water at 20° C.   
     
     
       2. The composition of claim 1 wherein the copolymer resins in the copolymer resin emulsions [A] and [B] have an average particle diameter in the range of from 0.25 to 0.60 micron. 
     
     
       3. The composition of claim 1 wherein the ester (a) or (a)' is at least one member selected from the group consisting of C 1  -C 10  alkyl esters of acrylic acid, C 1  -C 10  alkyl esters of methacrylic acid, glycidyl esters of acrylic acid, glycidlyl esters of methacrylic acid, hydroxy-(C 1  -C 4 )alkyl esters of acrylic acid and hydroxy-(C 1  -C 4 )alkyl esters of methacrylic acid. 
     
     
       4. The composition of claim 1 wherein the alpha, beta-unsaturated carboxylic acid (b) or (b)' is at least one member selected from the group consisting of alpha, beta-unsaturated carboxylic acids having 3, 4 or 5 carbon atoms and anhydrides thereof. 
     
     
       5. The coating composition of claim 1 wherein the water-soluble polyvalent metal salt [C] is at least one metal salt selected from the group consisting of lower aliphatic carboxylic acid salts, hydrochlorides, sulfates and nitrites of divalent or trivalent metals. 
     
     
       6. The coating composition of claim 1 wherein the total solids resin content of the copolymer resin emulsions [A] and [B] is about 30 to about 70% by weight based on the total weight of the emulsions [A] and [B]. 
     
     
       7. The coating composition of claim 1 which further comprises at least one additive selected from the group consisting of other water-dispersible resins, fillers, coloring agents, antiseptics, dispersing agents, thickening agents, thixotropic agents, antifreezing agents and pH adjusting agents. 
     
     
       8. The composition of claim 1 wherein the esters (a) and (a)' are independently selected from the group consisting of methylacrylate, ethylacrylate, butylacrylate, 2-ethylhexylacrylate, methylmethacrylate, butylmethacrylate, 2-ethylhexylmethacrylate and mixtures thereof; and wherein the alpha,beta-unsaturated carboxylic acids (b) and (b)' are each independently selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid and mixtures thereof.